Blast closure



1966 D. T. GUNDERSEN 3,278,154

BLAST CLOSURE Filed Sept. 5, 1963 5 Sheets-Sheet l 'INVENTOR flan/e! 7. 6401060? Allan, e

Oct. 11, 1966 D. T. GUNDERSEN BLAST CLOSURE 5 Sheets-Sheet 2 Filed Sept. 5. 1963 m I M; g T a 3 v 7 3 2 Z W M Q e a a z Q T 6 L. I :L Q

INVENTOR.

'andbrson @244 G W Illa/nay Oct. 11, 1966 D. T. GUNDERSEN BLAST CLOSURE Filed Sept. 5, 1963 5 Sheets-Sheet 5 INVENTOR.

M 8 m 7 f 1% M Oct. 11, 1966 u s N 3,278,154

BLAST CLOSURE Filed Sept. 5, 1963 5 Sheets-Sheet 4 INVENTOR. 0a/el 7. aunae/sen BYMQ.W

lf/orney This invention relates to a blast closure which is particularly adapted for use in the presence of extreme atmospheric overpressures, such as those generated by an atomic blast or by large quantities of high explosives.

It is the primary object of the invention to provide a blast closure which is capable of withstanding the shock eifects resulting first from the blast and second from the operation of the closure itself.

it is a further object of the invention to provide a blast closure which is operated automatically by the overpressur created by a blast.

In essence, my invention contemplates a blast closure in which a movable member, such as a piston or the like, is driven toward closed position within a chamber by an extreme atmospheric overpressure or blast wave. At the same time, part of the atmospheric overpressure created by the blast is permitted to enter the chamber. As the blast pressure enters the chamber, the pressure of the chamber rapidly becomes equal to the pressure acting upon the piston. As the piston compresses the air within the chamber, the chamber pressure increases to an amount substantially greater than the diminishing blast pressure which is acting to move the piston toward closed position. This higher chamber pressure, which results from combining the atmospheric overpressure with an increase in pressure generated by movement of the piston toward closed position, acts to snub the piston movement and prevent any impact damage resulting from too rapid movement of the piston toward closed position. As the piston approaches its closed position, the chamber pressure is greater than the outside pressure, so it leaks out and is reduced until it becomes equal to the outside pressure.

It is accordingly an object of my invention to provide a blast closure which utilizes the principles of operation et forth above.

it is a further object of the invention to provide blast closures of the type described which are designed for a fixed high pressure, which are designed for a range of high pressures, and which are designed for both high and low pressure operation.

It is a more particular object of my invention to provide such a blast closure in which frictional components are reduced as far as possible, in order to assure proper functioning of the closure at all times.

My invention also comprises such other objects, advantages and capabilities as will later more fully appear from the following detailed description of my invention and which are inherently possessed by my invention.

While I have shown in the accompanying drawings preferred embodiments and illustrations of my invention, it should be understood that the same are susceptible of many variations, modifications, and changes, without departing from the spirit of my invention.

Referring to the drawings, FIG. 1 is a longitudinal sectional view of a blast closure constructed in accordance with my invention, with the passage which is selectively opened or closed by the closure movement shown in the lower part of the figure;

FIG. 2 is a sectional view of the same, taken along line 2-2 of FIG. 1;

FIG. 3 is a longitudinal sectional view of an alternative embodiment of blast closure;

FIG. 4 is an enlarged transverse sectional view of the same, taken along line 4-4 of FIG. 3;

ited States Patent C) FIG. 5 is a schematic view of my blast closure in use, at the moment before the blast pressure strikes the piston;

FIG. 6 is a schematic view of the same, after the blast pressure strikes and moves the piston and also enters the chamber;

FIG. 7 is a schematic view showing the relationship of the components when the chamber pressure becomes substantially equal to the pressure acting upon the piston;

FIG. 8 is a schematic view showing the piston approaching closed position, as pressure moves out of the chamber past the piston;

FIG. 9 is a schematic view showing the piston in substantially closed position, with the pressure in the lower chamber being bled oif;

FIG. 10 is a schematic view of an alternative embodiment of my invention, in which the passage which permits the exchange of pressure between the chamber and the atmosphere is independent from the piston, instead of surrounding it as in the other embodiments shown;

FIG. 11 is a composite schematic view and graph, showing the relative relationship between the piston movement, blast pressure and chamber pressure during operation of the blast closure.

One embodiment which has been selected to illustrate my invention comprises a housing 10, having an opening it at the upper end thereof which is exposed to the blast pressure. A piston 12 is mounted for sliding movement within the housing it The piston 12 includes a head 13, which is mounted on the upper end of a shaft 14. A valve closure member 15 is mounted on the lower end of the shaft 14.

A pin it? extends downwardly from the bottom of the shaft 14. A coil spring 17 concentrically surrounds the pin 26. The lower end of the spring 17 bears against the inside of the bottom of the housing it and its upper end extends into an opening 18 in the bottom of the shaft 14. The spring 17 normally urges the piston 12 toward its upper position, as shown in FIG. 1 of the drawings.

Extending transversely to the lower part of the housing it) is a delay duct entrance 19 and exit Zn. In its closed position, the valve closure member 15 closes off the connection between the delay duct entrance 19 and exit 20. When the valve closure member 15 is in open position, as shown in FIG. 1 of the drawings, the entrance 19 and exit 24) are connected by openings 38 in the lower part of the housing 10.

The top of the piston head 13 has an outer diameter which is slightly less than the inner diameter of the adjacent walls of the housing it leaving a small circular orifice 21 between them. Two diametrically opposed sides of the head 13 are cut away to form a pair of open sectors 22. A closure plate 23 is slidably mounted beneath a pair of holding bars 24, which are secured to the top of the head 13 adjacent to the open sectors 22. The ends of the closure plate 23 are arcuate and normally extend radially outwardly from the head 13 to close ofi the open sectors 22.

The upper end of the head 13 is dished out to form a recess 25. A pair of leaves 26 and 27 are mounted within the recess 25'. The leaves 26 and 27 are spaced slightly from each other and have their opposite ends engaging the Walls of the recess 25. The closure plate 23 and the leaves 26 and 27 are all slidably mounted on a pair of vertically directed pins 23.

The lower part of the head 13 is substantially hemispherical. The upper part of the housing 10 beneath the head 13 is open, forming a chamber 36, the lower part of which is rounded complementarily to the bottom of the head 13.

A passage 31 concentrically surrounds the shaft 14 and is normally closed off by a resilient check seal 32. The

passage 31 connects the chamber 30 to an open dashpot area 39, which is formed Within the housing directly above the valve closure member 15.

The upper end of the valve closure member 1s provided with a circular resilient seal 33, which extends outwardly to engage the adjacent inner side wall of the housing 10. The lower end of the valve closure member 15 is provided with an outwardly directed peripheral flange 34, which engages an adjacent transverse port1on 35 of the housing 10, to limit the upward movement of the piston 12 within the housing 10. An annular resilient packing 36 seals and cushions the engagement between the flange 34 and the housing 10. Downward movement of the piston 12 is limited by engagement between the flange 34 and another transverse portion 37 of the housing 10 and/ or by engagement between the lower part of the head 13 and the bottom of the chamber 30.

In order to provide a minimum amount of frictional engagement between the piston 12 and the housing 10, the head 13 and the valve closure member 15 are both provided with a plurality of balls 40, which are mounted in the outer ends of recesses 41 disposed adjacent to the periphery of the head 13 and valve closure member 15. Each ball 40 is normally urged outwardly by a coil spring 42, mounted Within the recess 41, which urges the ball 40 into or toward engagement with the adjacent wall of the housing 10. The balls 40 provide practically frictionless engagement between the piston 12 and the housing 10.

An L-shaped bleed opening 43 is provided in the upper part of the valve closure member 15, to connect the dashpot area 39 with the delay duct entrance 19. The size of the bleed opening 43 is controlled by adjustment of a set screw 44, which intersects the corner of the bleed opening 43.

When an overpressure strikes the closure plate 23, it deflects the center of the closure plate 23 downwardly into the recess 25. As the center of the closure plate 23 moves downwardly, its opposite ends are pulled inwardly to permit the overpressure to move through part of the open sectors 22 as well as the orifice 21. As the center of the closure plate 23 continues to move downwardly, it will strike the uppermost leaf 26. The leaf 26 acts as a re-enforcement for the center of the closure plate 23, which can be deflected further downwardly only if the pressure is sufficiently high to deflect both the closure plate 23 and the leaf 26.

The second leaf 27 acts as a second cumulative re-enforcement in the same manner. The maximum opening adjacent to the piston head 13 accordingly occurs only when the closure plate 23 and both leaves 26 and 27 have been fully deflected downwardly into the recess 25. This construction is adapted for use over a substantial range of high pressures, with the size of the orifice adjacent to the piston head being directly related to the amount of pressure.

An alternative embodiment of my invention is shown in FIGS. 3 and 4 of the drawings. This embodiment of my invention comprises a housing 50 having an open upper end 51, which is exposed to atmospheric pressure. A piston 52 is mounted for sliding movement within the housing 50. The piston 52 includes a piston head 53 and a shaft 54. A valve closure member 55, which is carried by the shaft 54, in its extreme downward closed position engages the transverse portions 90 and closes off openings 56 in the housing 50 from the exit 91. A coil spring 57 concentrically surrounds the shaft 54 and extends between the upper part of the valve closure member 55 and the lower part of the housing 50. The spring 57 normally urges the piston 42 upwardly within the housing 50.

The detailed structure of the head 43 is best seen in FIG. 4 of the drawings. As shown, the periphery of the head 53 is divided into two parts, between which are held a resilient seal 58, which extends radially outwardly response to high and low pressures will be described hereinafter.

In order to provide substantially frictionless but guided movement of the piston 52 within the housing 50, a plurality of wheel assemblies are provided on the piston head 53 and the valve closure member 55. These assemblies are also best seen in FIG. 4 of the drawings.

Each of the assemblies includes a U frame 62, within which is mounted a pre-compressed coil spring 63, which has been loaded to a predetermined amount commensurate with the amount of impact to be absorbed in order to prevent excessive lateral movement of the piston 52. A shaft 64 extends through the spring 63 and carries at its outer end a wheel (or ball) 65. There is preferably a slight clearance between the periphery of the wheel 65 and the inner wall of the housing 50.

The other end of the coil spring 63 bears against a collar 66, which is pinned to the shaft 64. When the wheel 65 starts to move inwardly, it must move against the load already imposed upon the spring 63 plus the additional load imposed by further compression of the spring 63 as the collar 66 moves inwardly.

The upper and lower ends of the valve closure member 55 are sealed off by annular resilient seals 67 and 68 respectively. An upper chamber 69 is provided within the upper part of the housing 50, beneath the piston head 53. The chamber 69 is connected by a passage 70 to a dashpot area 71 above the valve closure member 55. A resilient seal 72 normally closes off the passage 70. An L-slhaped bleed 73 in the upper part of the valve closure member 55 is adjusted by a set screw 74.

If a low pressure strikes the piston head 53, the force will not be sufiicient to deflect the resilient seal 58 and metal members 59 and the device will accordingly function only in the manner of a conventional impact absorber in that the chamber 69 will remain sealed against and insulated from the pressure acting upon the piston head 53.

If a high pressure strikes the piston head 53, the resilient seal 58 and metal members 59 are deflected inwardly into the adjacent recessed area defined by the curved walls 60, opening an orifice surrounding the piston head 53. High pressure passes through this orifice into the chamber 69 and the device then operates in the manner taught bv this invention, in that the pressure is leaked into and out of the chamber 69 and is compressed to provide a chamber pressure greater than that acting upon the piston, so as to brake the piston movement. This embodiment of my invention is accordingly adapted to operate in a conventional manner at low pressures and in the manner taught by the present invention at high pressures.

The operation of my invention in use can best be understood by reference to the series of schematic drawings FIGS. 5-9, inclusive. Referring first to FIG. 5, this shows the structural elements in the same positions in which they are shown in FIGS. 1-4 of the drawings. For convenience, the reference numerals of the embodiment shown in FIGS. 1-2 have been applied to the upper part of FIGS. 5-9 and the reference numerals of FIGS. 3-4 have been applied to the lower part of FIGS. 5-9, since the movements and relationships indicated in FIGS. 59 are equally applicable to both embodiments of my invention.

Referring now to FIG. 6 of the drawings, as a high pressure blast strikes the piston head 13-53, it moves inwardly within the chamber 14'52 of the housing 1050. In the embodiment of my invention shown in FIGS. 1 and 2, the high pressure also strikes the closure plate 23 on the top of the piston head -13 and causes it to move downwardly within the recess 25. This retracts the opposite ends of the closure plate 23, opening the open sectors 22, to provide an orifice through which the blast pressure can enter the chamber 311.

In the second embodiment of my invention, which is shown in FIGS. 3-4, the high pressure strikes the resilient seal 51 and metal members 59 and 61B and bends them back along the inner curved walls 611, to provide an orifice through which the blast pressure can enter the chamber as.

Both of these movement are indicated schematically on FIG. 6 by showing inward movement of the orifice seal, with arrows designating flow of the blast pressure into the chamber. Entry of the blast pressure into the chamber also results in the movement of air from the chamber 311-69 through the passage 31-71 past the check seal 32-72 and into the dashpot area 39-71. The blast pressure also :acts to move the piston 14-52 inwardly against the pressure of the coil spring 113-57.

Referring now to FIG. 7 of the drawings, this indicates the condition which results when the flow of blast pressure into the chamber Fail-59, plus the compressive action resulting from the inward movement of the piston 14-52, results in the chamber pressure being equal to that outside the chamber. At this time, there is no movement of air into the chamber, and this is indicated schematically by the closed seals around the piston head and by the absence of arrows showing air flow into the chamber.

Air will still continue to move out of the chamber 30-69 through the passage 31-711 and into the dashpot area 3Q-71, because the pressure in the chamber SW69 is greater than that in the dashpot area 35-71. The piston 14- 2 continues to move further inwardly against the pressure of the spring 16-57.

Referring now to FIG. 8 of the drawings, it will be seen that the piston head 13-53 continues to move inwardly due to the force of momentum, even though the pressure resisting its inward movement is greater than the pressure urging it inwardly. The pressure within the chamber 30-69 will accordingly be increased by the compressive action of the piston head 213-53, while at the same time the blast pressure outside continues to diminish due to the passing or dissipation of the blast wave. The chamber pressure is accordingly greater than the outside pressure and air flows out from the chamber 39-69 to the outside. The pressure within the chamber 30-69 is still greater than that within the dashpot area 39-71 and air will accordingly continue to flow through the passage 31-711 past the check seal 32-72.

It will be noted that the movement of the blast pressure down the delay duct to the delay duct entrance 19 is sufficiently delayed in time by the length of the delay duct, so that the blast pressure will not strike the openings 38-56 in the housing -50 until they are closed off by movement of the valve closure member -55 to closed position.

Referring now to FIG. 9 of the drawings, this shows the piston 14-52 in closed position, with the piston head 13-53 being disposed at the bottom of the chamber 31 69. The openings 38-56 are closed off by the closure member 15-55, as the blast pressure arrives through the delay duct. The only movement of air is from the dashpot area through the bleed opening 43-73.

The compressed spring 16-57 tends to urge the piston 14-52 back toward open position. However, the air which is trapped within the dashpot area 39-71 acts to snub and slow down the opening movement of the piston 14-52, so as to delay the opening of the piston until after the blast wave has passed. This snubbing action is controlled by adjustment of the set screws 4- 1-74, which control the rate of flow of pressure from the dashpot area 39-71 out through the bleed 43-73 and which accordingly control the speed of closing movement of the piston 1- 1-52.

If desired, locking or latching means may be provided iii which will engage automatically upon the closing of the piston 14-52 and which will hold it in closed position until the holding means is released.

FIG. 10 of the drawings shows a schematic diagram of another embodiment of my invention which is substantially identical with those previously shown and described, but in which a separate passage 811! is provided, which is completely independent from the piston head 81, instead of surrounding it as in the previous embodiments. The passage fill leads into a chamber 82 and the action and structure of the device is otherwise similar to that described above.

It should be understood that in any and all embodiments of the invention, the orifice or opening through which the blast pressure enters the chamber must be carefully calculated in order to provide the desired eifect and action. The size of the orifice must necessarily be proportionate to the blast pressure. If a fixed orifice is used, the device will operate satisfactorily only over a limited range of pressures on opposite sides of the calculated or optimum anticipated pressure. Suitable means may be provided, however, either in the form shown in FIGS. 1 and 2 of the drawings or in any other suitable form, for adjusting (either automatically or otherwise) the size of the orifice to the blast pressure.

FIG. 11 of the drawings illustrates the operation of the invention by means of a combined schematic diapressure and then continues to build up to an amount far greater than the blast pressure. Its buildup finally stops, due to the leakage of pressure out of the chamber and the slowing of the piston movement, so that the chamber pressure falls rapidly back to an amount equal to the blast pressure.

The schematic drawing at the top of FIG. 11, which is coordinated with the graph below, shows that the blast pressure leaks into the chamber during approximately the first half of the piston movement, stops when the blast and chamber pressures are equal, and pressure then leaks out of the chamber during approximately the last half of the piston movement.

Referring to FIGS. 3 and 4 of the drawings, when the blast pressure within the chamber 69 is equal to the outside pressure, the resilient seal 53 and metal members 55 return to the position shown in FIG. 4 of the drawings. When the pressure within the chamber 69 becomes greater than the blast pressure, the resilient seal 53 and metal members 59 are flexed outwardly against the outside curved walls 619, to permit the flow of air out of the chamber 69.

In operation, the pressure in the chamber at the half stroke of the piston is preferably approximately equal to the blast pressure.

The variables which are involved in the construction and operation of the device and their method of measurement are as follows:

W=Weight of piston assembly in pounds. A =Piston area in square feet.

A =Chamber area in square feet.

A=Orifice area in square feet.

S=Piston stroke in feet.

P =Blast pressure in pounds per square foot. P =Ambient pressure in pounds per square foot. v=Velocity of flow in feet per second. T =Ambient temperature in degrees Fahrenheit. D =Piston diameter in feet.

D =Chamber diameter in feet.

7 Applicable relationships (a) F=ma (e) m =W/g (b) s= /2at (f) V=A XS (c) A=D /4 (g) a==(P A)/(W/g) (d) F=P A (h) P V =Constant For high blast pressures the original pressure volume may be neglected. The speed v equals the critical speed v of 1050 feet per second at a temperature of 60 F. whenever the blast pressure is equal to or greater than 1.9 times the ambient pressure.

The equations which are applicable for determining the physical size and relationships of the component parts are as follows:

Utilizing these formulas in a specific example, for a given blast pressure (P of 1000 pounds per square foot, a piston assembly weight (W) of 1000 pounds, a stroke (S) of 1 foot, a velocity (v) of 1050 feet per second and a piston diameter (D of 4 feet, the additional clearance (AD) required for the chamber diameter (D may be calculated as follows:

It will be noted from the above formulas that the dif ference in the diameter of the orifice is proportional to the square root of the blast pressure, to the square root of the stroke, to the square of the piston diameter and inversely proportional to the velocity of the flow.

I claim:

1. In a blast closure, a housing having an opening at the upper end thereof which is exposed to blast pressure, a piston mounted for sliding movement within said housing, said piston having a head extending across and normally closing substantially all of said opening, a chamber within said housing beneath said piston head, said piston being mounted for inward movement by the force of blast pressure acting upon said piston head, an orifice connecting said chamber to the blast pressure, the size of said orifice being so proportioned to the blast pressure and the speed of inward movement of said piston in response thereto as to permit said blast pressure to enter said chamber and increase the pressure therein to an amount substantially equal to that of the blast pressure, while thereafter restricting the flow of air out of said chamber so that the inward movement of said piston compresses the air within said chamber and increases the pressure within said chamber to an amount substantially greater than that of the blast pressure, said increased pressure acting against said piston head in opposition to the blast pressure to snub the inward movement of said piston and prevent damage to said closure, said housing having a dashpot area disposed inwardly from said chamber, a valve closure member carried by said piston and having a portion acting as a piston within said dashpot area, a passage connecting said chamber to said dashpot area, sealing means for permitting the flow of air from said chamber to said dashpot area and preventing the flow of air from said dashpot area to said chamber, and means carried by said valve closure member for providing a closure upon the movement of said piston to its inward position.

2. In a blast closure, a housing having an opening at the upper end thereof which is exposed to blast pressure, a piston mounted for sliding movement within said housing, said piston having a piston head extending across and substantially closing said opening, a chamber within said housing disposed inwardly from said piston head, said piston head being mounted adjacent the outer end of a shaft, an open dashpot area formed within said housing inwardly from said chamber, a valve closure member carried by said shaft and disposed within said dashpot area, said valve closure member being adapted to provide a closure upon the movement of said piston to its inward position, a passage adjacent said shaft connecting said chamber to said dashpot area, check sealing means extending across said passage to permit the flow of pressure only from said chamber into said dashpot area, resilient means acting to normally urge said piston toward its outward position, sealing means to prevent the flow of pressure out of said dashpot area, and substantially frictionless engaging means between said piston and housing, said piston adapted to be moved inwardly by the force of blast pressure acting upon said piston head, an orifice disposed between said piston head and the walls of said housing, the size of said orifice being so proportioned to the blast pressure and the speed of inward movement of said piston in response thereto as to permit said blast pressure to enter said chamber and increase the pressure therein to an amount substantially equal to that of the blast pressure, while thereafter restricting the fiow of air out of said chamber so that the inward movement of said piston compresses the air within said chamber and increases the pressure within said chamber to an amount substantially greater than that of the blast pressure, said increased pressure acting against said piston head in opposition to the blast pressure to snub the inward movement of said piston and prevent damage to said closure.

3. The structure described in claim 2, said substantially frictionless engaging means comprising a plurality of rotatable members carried by said piston head and valve closure member, each of said rotatable members having a resilient means normally urging said rotatable member toward engagement with said housing.

4. The structure described in claim 2, and a bleed opening extending from said dashpot area to control the flow of pressure from said dashpot area and regulate the return movement of said piston to its outward position, and adjusting means for controlling the size of said bleed opening.

5. In a blast closure, a housing having an opening at the upper end thereof which is exposed to blast pressure, a piston mounted for sliding movement within said housing, said piston having a piston head extending across and substantially closing said opening, an orifice disposed between said piston head and the adjacent walls of said housing, a chamber within said housing disposed inwardly from said piston head, said piston head being mounted adjacent the outer end of a shaft, an open dashpot area formed within said housing inwardly from said chamber, a valve closure member carried by said shaft and having a portion act as a piston within said dashpot area, said valve closure member being adapted to provide a closure upon the movement of said piston to its inward position,

a passage adjacent said shaft connecting said chamber to said dashpot area, resilient means acting to normally urge said piston toward its outward position, said piston being mounted for inward movement by the force of blast pressure acting upon said piston head, said blast pressure passing through said orifice into said chamber and being compressed by the inward movement of said piston head to provide a pressure within said chamber substantially greater than said blast pressure to snub the inward movement of said piston and prevent damage to said closure.

6. The structure described in claim 5, and substantially frictionless engaging means between said piston and housing to facilitate the sliding movement of said piston within said housing, said engaging means comprising a plurality of spaced rotatable members resiliently urged toward engaging position.

7. The structure described in claim 5, said piston head having at least one open sector, closure means carried by said piston head normally extending across said open sector, said closure means being constructed and arranged so as to remain closed at a given pressure and to be opened by a higher pressure, to increase the size of said orifice and the flow of blast pressure into said chamber in proportion to the amount of blast pressure.

8. The structure described in claim 7, said piston head having a recess in the outer end thereof, a closure plate extending across said recess and having an end thereof normally overlying and closing off said open sector, the midportion of said closure plate being adapted to be deflected downwardly into said recess by said blast pressure, to retract the end of said closure plate and open said open sector to permit the flow of blast pressure therethrough.

9. The structure described in claim 8, and at least one leaf mounted between said closure plate and the bottom of said recess, said leaf-reenforcing said closure plate and adapted to be deflected downwardly into said recess by said closure plate.

10. In a blast closure, a chamber, an operating mem ber inwardly movable with respect to said chamber in response to the blast pressure, an orifice connecting said chamber to the blast pressure to raise the pressure within said chamber to an amount substantially equal to the blast pressure, the inward movement of said operating member being adapted to compress the air within said chamber and increase the pressure within said chamber to an amount substantially greater than the blast pressure, said increased pressure within said chamber acting against said operating member in opposition to the blast pressure to snub the inward movement of said operating member in response to the blast pressure and prevent damage to said closure, a dashpot connected to said chamber, and means connecting the pressure from said chamber into said dashpot, said dashpot acting to control the return movement of said operating member.

References Cited by the Examiner UNITED STATES PATENTS 618,903 2/1899 Prince 137-514.7 X 1,583,404 5/1926 Lovejoy. 2,777,465 1/1957 Adams 137-5147 X 2,877,750 3/1959 Maier -261 2,954,047 9/ 1960 Faltejsek 137-494 3,075,448 1/1963 Cohen 98-1 M. CARY NELSON, Primary Examiner.

A. JAFFE, E. FEIN, Assistant Examiners. 

1. IN A BLAST CLOSURE, A HOUSING HAVING AN OPENING AT THE UPPER END THEREOF WHICH IS EXPOSED TO BLAST PRESSURE, A PISTON MOUNTED FOR SLIDING MOVEMENT WITHIN SAID HOUSING, SAID PISTON HAVING A HEAD EXTENDING ACROSS AND NORMALLY CLOSING SUBSTANTIALLY ALL OF SAID OPENING, A CHAMBER WITHIN SAID HOUSING BENEATH SAID PISTON HEAD, SAID PISTON BEING MOUNTED FOR INWARD MOVEMENT BY THE FORCE OF BLAST PRESSURE ACTING UPON SAID PISTON HEAD, AN ORIFICE CONNECTING SAID CHAMBER TO THE BLAST PRESSURE, THE SIZE OF SAID ORIFICE BEING SO PROPORTIONED TO THE BLAST PRESSURE AND THE SPEED OF INWARD MOVEMENT OF SAID PISTON IN RESPONSE THERETO AS TO PERMIT SAID BLAST PRESSURE TO ENTER SAID CHAMBER AND INCREASE THE PRESSURE THEREIN TO AN AMOUNT SUBSTANTIALLY EQUAL TO THAT OF THE BLAST PRESSURE, WHILE THEREAFTER RESTRICTING THE FLOW OF AIR OUT OF SAID CHAMBER SO THAT THE INWARD MOVEMENT OF SAID PISTON COMPRESSES THE AIR WITHIN SAID CHAMBER AND INCREASES THE PRESSURE WITHIN SAID CHAMBER TO AN AMOUNT SUBSTANTIALLY GREATER THAN THAT OF THE BLAST PRESSURE, SAID INCREASED PRESSURE ACTING AGAINST SAID PISTON HEAD IN OPPOSITION TO THE BLAST PRESSURE TO SNUB THE INWARD MOVEMENT OF SAID PISTON AND PREVENT DAMAGE TO SAID CLOSURE, SAID HOUSING HAVING A DASHPOT AREA DISPOSED INWARDLY FROM SAID CHAMBER, A VALVE CLOSURE MEMBER CARRIED BY SAID PISTON AND HAVING A PORTION ACTING AS A PISTON WITHIN SAID DASHPOT AREA, A PASSAGE CONNECTING SAID CHAMBER TO SAID DASHPOT AREA, SEALING MEANS FOR PERMITTING THE FLOW OF AIR FROM SAID CHAMBER TO SAID DASHPOT AREA AND PREVENTING THE FLOW OF AIR FROM SAID DASHPOT AREA TO SAID CHAMBER, AND MEANS CARRIED BY SAID VALVE CLOSURE MEMBER FOR PROVIDING A CLOSURE UPON THE MOVEMENT OF SAID PISTON TO ITS INWARD POSITION. 